This hammer is made of a single piece of metal, including the handle, and is hollow even though it weighs the same as any other hammer. It has a hole on each end of the head and when swung makes a sound akin to a muffled warcry.
On a successful hit with this weapon the target creature and all creatures within 5 feet except yourself take thunder damage equal to your proficiency modifier, as it creates a loud gong-like smash.
On a critical failure with this weapon the concussion vibrates through your arms and you take 1d10 thunder damage.
Other weapons of this type exist, such as Roaring Maul of Resonance, and Roaring Flail of Resonance, but warhammers are the most common.